MONDAY, May 15, 2017 (HealthDay News) -- Women who entered menopause early or who never gave birth might have an increased risk of heart failure, a new study suggests.

Researchers analyzed data from more than 28,000 postmenopausal women who did not have heart disease at the start of the study. During an average follow-up of about 13 years, just over 5 percent of the women were hospitalized for heart failure.

Menopause usually occurs after age 45, but changes can start several years before a woman's periods end.

In the study, earlier menopause was associated with increased risk of heart failure, and this link was stronger in women who had natural rather than surgical menopause. But the researchers did not establish a cause-and-effect link.

Also, women who never gave birth seemed at increased risk for a type of heart failure in which the left side of the heart fails to relax as it should. This association was not due to infertility, researchers said.

Having more children was not associated with heart failure risk, according to the study published May 15 in the Journal of the American College of Cardiology.

"Our finding that a shorter total reproductive duration was associated with a modestly increased risk of heart failure might be due to the increased coronary heart disease risk that accompanies early menopause," senior author Dr. Nisha Parikh said in a journal news release. Parikh is an assistant professor at the University of California, San Francisco School of Medicine.

Previous studies found that sex hormones present during a woman's childbearing years may affect heart disease risk. Levels of these hormones may be affected by menstrual cycling and pregnancy.

In an editorial published with the study, cardiologist Dr. Nandita Scott said the mechanisms behind the findings are unclear, but their potential impact on women's health is important. She is co-director of the Corrigan Women's Heart Health Program at Massachusetts General Hospital.

"There also remain many unresolved questions including the mechanisms of estrogen's cardioprotective effect, making this truly a work in progress," she said. "Altogether, these findings raise interesting questions about the cardiometabolic effects of sex hormone exposure over a women's lifetime and continue to raise important questions for future research."